A preparation method of a hard carbon negative electrode material for ultra-high rate performance sodium ion battery

Abstract

The present disclosure belongs to the technical field of material preparation, and specifically provides a preparation method of a hard carbon negative material for a super-high rate performance sodium ion battery. The interlayer spacing of the hard carbon derived from thermosetting phenolic resin is effectively improved by low-temperature carbonization of the thermosetting phenolic resin, the obtained hard carbon material can reach an interlayer spacing of 0.399 nm, and the surface groups of the hard carbon are eliminated by microwave pulse treatment. The non-thermal effect (not more than 200 DEG C) of microwave treatment is not enough to cause the interlayer spacing of the hard carbon to be narrowed, so that the first coulomb efficiency is greatly improved as the electrode side reaction is greatly reduced. The first coulomb efficiency of the hard carbon reaches 90.2% at 100 mA / g, and the reversible sodium storage capacity is 294, 270, 250, 200, 180 and 150 mAh / g at current densities of 0.1, 0.2, 0.5, 1, 2 and 5 A / g, respectively. The prepared hard carbon has high rate and high first efficiency sodium storage performance. And it shows fast sodium storage performance and super-high first coulomb efficiency.

Description

Technical Field

[0001] This disclosure relates to the field of materials preparation technology, and in particular to a method for preparing hard carbon anode materials for ultra-high rate performance sodium-ion batteries. Background Technology

[0002] Energy sources such as wind and solar power face the challenge of storage and utilization. Although lithium-ion batteries have long been used as energy storage devices, Earth's lithium resources are extremely limited, making them unsuitable for large-scale energy storage. Sodium ions, on the other hand, are abundant on Earth, making the development of next-generation sodium-ion batteries a very promising energy storage solution. As an advanced next-generation energy storage device, the development of high-energy sodium-ion batteries requires high-capacity positive and negative electrodes. Since 2010, sodium-ion batteries have been extensively studied as a novel battery system due to their naturally abundant sodium content and a wide variety of available sodium compounds compared to lithium. In recent years, many high-energy-density sodium-ion battery materials based on these abundant elements have been reported. In the development of sodium-ion battery negative electrode materials, carbon materials have received considerable attention, similar to those used in lithium-ion batteries. The structural control of carbon-based materials for energy storage applications in both lithium-ion and sodium-ion batteries is a recent goal. Several attractive carbonaceous materials, such as graphite, carbon nanowires, hollow carbon nanowires, hollow carbon spheres, and hard carbon, have been extensively studied as negative electrode materials. Hard carbon, with its large interlayer spacing (>3.4 nm), is ideal for sodium storage, allowing sodium ions to freely enter and exit the interlayer spaces. However, the structure of hard carbon is highly dependent on synthesis conditions, often requiring temperatures above 1500℃ (excessive temperatures tend to produce hard carbon with smaller interlayer spacing), while excessively low temperatures result in hard carbon with more functional groups, leading to significant side reactions that consume lithium ions, resulting in a lower initial coulombic efficiency (43.7%). Therefore, further research into controlling synthesis conditions can improve the electrochemical performance of hard carbon electrodes. To achieve rapid sodium storage and good rate performance, hard carbon with a high interlayer spacing needs to be prepared. To improve its initial efficiency, hard carbon materials with fewer functional groups must be prepared. Therefore, developing a hard carbon anode material with high initial efficiency and high rate performance for sodium-ion batteries is a very forward-looking idea. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing hard carbon anode materials for ultra-high rate performance sodium-ion batteries.

[0004] In a first aspect, the present invention provides a method for preparing a hard carbon sodium-ion battery anode material with high layer spacing and fewer surface groups at a lower temperature, which is obtained by low-temperature carbonization of thermosetting phenolic resin under an inert atmosphere and further microwave treatment.

[0005] Preferably, the thermosetting phenolic resin is heated and carbonized in an inert atmosphere to obtain hard carbon with a high interlayer spacing, and then the hard carbon is microwaved in an inert atmosphere to eliminate functional groups.

[0006] Preferably, the carbonization conditions for thermosetting phenolic resin are as follows: the phenolic resin is carbonized in a box furnace under a nitrogen atmosphere with a nitrogen flow rate of 1-100 L / min, at a heating rate of 0.5-20 °C / min, to 600-800 °C, and held for 1-12 h.

[0007] Preferably, the conditions for eliminating radicals by microwave treatment of hard carbon under an inert atmosphere are as follows: the hard carbon is microwaved with a power of 700W for 6-240s in an argon atmosphere in a microwave oven to eliminate radicals, and the microwave treatment temperature does not exceed 200℃.

[0008] Secondly, this invention provides a method for preparing a hard carbon sodium-ion battery anode material with high layer spacing and few surface groups at a relatively low temperature. The specific steps are as follows:

[0009] Step 1: Carbonize the thermosetting phenolic resin in a box furnace at a set flow rate under an inert atmosphere, by heating to a set temperature at a set rate and holding for a set time.

[0010] Step two, the obtained hard carbon with high-level spacing is then subjected to group elimination in a microwave oven under an inert atmosphere and microwave pulsed at a set power for a set time.

[0011] Step 3: Natural cooling. Finally, the carbon material is removed from the microwave oven to obtain a hard carbon sodium-ion battery anode material synthesized at a lower temperature with high layer spacing and fewer surface groups.

[0012] Preferably, in step one, the thermosetting phenolic resin is carbonized in a box furnace at a set flow rate under an inert atmosphere, through a set heating rate to a set temperature and held for a set time; the inert atmosphere gas is nitrogen.

[0013] Preferably, in step one, the thermosetting phenolic resin is carbonized in a box furnace under an inert atmosphere at a set flow rate, through a set heating rate to a set temperature, and held at that temperature for a set time; the inert gas flow rate in the box furnace is 1-100 L / min.

[0014] Preferably, in step one, the thermosetting phenolic resin is carbonized in a box furnace under an inert atmosphere at a set flow rate, through a set heating rate to a set temperature, and held at that temperature for a set time; the set heating rate is 0.5-20℃ / min.

[0015] Preferably, in step one, the thermosetting phenolic resin is carbonized in a box furnace under an inert atmosphere at a set flow rate, through a set heating rate to a set temperature, and held at that temperature for a set time; the set temperature is 600-800℃.

[0016] Preferably, in step one, the thermosetting phenolic resin is carbonized in a box furnace under an inert atmosphere at a set flow rate, through a set heating rate to a set temperature, and held for a set time; the set holding time is 1-12 hours.

[0017] Preferably, in step two, the hard carbon undergoes radical elimination in a microwave oven under an inert atmosphere with microwave pulses at a set power for a set time; the inert atmosphere is argon.

[0018] As a preferred embodiment, in step two, the hard carbon undergoes radical elimination in a microwave oven under an inert atmosphere with microwave pulses at a set power for a set time; the microwave oven's pulse power is 700W.

[0019] As a preferred embodiment, in step two, the hard carbon is subjected to microwave pulse elimination at a set power for a set time in an inert atmosphere in a microwave oven; the set pulse time is 6-240s.

[0020] Preferably, in step two, the hard carbon is subjected to group elimination in a microwave oven under an inert atmosphere and with microwave pulses at a set power for a set time; the microwave treatment temperature does not exceed 200°C.

[0021] Thirdly, the present invention provides a method for preparing hard carbon anode material for ultra-high rate performance sodium-ion batteries.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] This invention involves low-temperature carbonization of thermosetting phenolic resin, effectively improving the interlayer spacing of thermosetting phenolic resin-derived hard carbon. The resulting hard carbon material achieves an interlayer spacing of 0.399 nm. Furthermore, microwave pulse treatment eliminates surface functional groups on the hard carbon. The non-thermal effects of microwave treatment (not exceeding 200°C) are insufficient to narrow the interlayer spacing, significantly reducing its role as an electrode side reaction and greatly improving the initial coulombic efficiency. The initial coulombic efficiency reaches 90.2% at 100 mA / g, and it exhibits reversible sodium storage capacities of 294, 270, 250, 200, 180, and 150 mAh / g at current densities of 0.1, 0.2, 0.5, 1, 2, and 5 A / g, respectively. The prepared hard carbon demonstrates high rate capability and high initial efficiency in sodium storage. Because the hard carbon material provided by this invention has a large interlayer spacing and few surface functional groups, the non-thermal effects of microwave treatment (not exceeding 200°C) are insufficient to narrow the interlayer spacing, thus exhibiting rapid sodium storage performance and ultra-high initial coulombic efficiency. Attached Figure Description

[0024] Figure 1 The images show the XRD diffraction patterns of hard carbon prepared in Example 1 and Comparative Example 1 of this invention.

[0025] Figure 2The first cycle curves of the hard carbon prepared in Example 1 and Comparative Example 2 of this invention at 100 mA / g are shown.

[0026] Figure 3 The diagram shows the rate performance of the hard carbon prepared in Example 1 and Comparative Example 1 of this invention at different current densities. Detailed Implementation

[0027] To better illustrate the process and solution of the present invention, the following description is provided in conjunction with the accompanying drawings and embodiments. The specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0028] This invention provides a method for preparing hard carbon anode material for ultra-high rate performance sodium-ion batteries, comprising the following steps:

[0029] S1, using thermosetting phenolic resin as the carbon source, is placed in a graphite crucible and heated and kept warm in a box furnace under a nitrogen flow to obtain a hard carbon material with a wide interlayer spacing.

[0030] S2, the hard carbon material with a wide interlayer spacing obtained in S1 is microwave pulsed in an argon atmosphere microwave oven for a period of time.

[0031] S3, after microwave treatment, the hard carbon is cooled naturally at room temperature in the microwave oven, thus obtaining a hard carbon material with wide interlayer spacing and fewer surface groups.

[0032] The above technical solution allows for the simple, low-cost, and environmentally friendly preparation of hard carbon materials with wide interlayer spacing and fewer surface groups, thereby improving sodium storage speed and efficiency. The principle behind the wide interlayer spacing and fewer surface groups in the hard carbon material obtained by this invention lies in: carbonizing phenolic resin at a lower temperature facilitates the formation of its disordered structure, thereby increasing the interlayer spacing of the carbon material. This results in a larger interlayer spacing in the hard carbon, enabling the hard carbon anode to achieve rapid sodium storage and improving its rate performance. Furthermore, based on the larger interlayer spacing, microwave treatment of the hard carbon allows the electric and magnetic fields of the microwaves to vibrate and break the chemical bonds of the surface groups, eliminating the surface groups generated during the low-temperature carbonization process. The non-thermal effects of microwave treatment (not exceeding 200°C) are insufficient to narrow the interlayer spacing of the hard carbon, thus reducing the generation of side reactions on the anode surface and improving coulombic efficiency.

[0033] Example 1

[0034] S1. Take 100g of thermosetting phenolic resin as a carbon source, put it into a graphite crucible, and heat it to 650℃ in a box furnace with a nitrogen flow of 10L / min and a heating rate of 5℃ / min and hold it for 2h to obtain 51.4g of hard carbon material with wide interlayer spacing.

[0035] S2, the 51.4g of hard carbon material with wide interlayer spacing obtained in S1 was placed in an argon atmosphere microwave oven and the surface groups were removed with a microwave pulse power of 700W for 60s.

[0036] S3, after microwave treatment, the hard carbon is allowed to cool naturally at room temperature in the microwave oven, resulting in 49.6g of hard carbon material with wide interlayer spacing and few surface groups.

[0037] Comparative Example 1

[0038] S1. Take 100g of thermosetting phenolic resin as a carbon source, put it into a graphite crucible, and heat it to 1500℃ in a box furnace with a nitrogen flow of 10L / min and a heating rate of 5℃ / min and hold it for 2h to obtain 49.8g of hard carbon material.

[0039] S2, 49.8g of hard carbon material obtained in S1 was placed in an argon atmosphere microwave oven and the surface groups were removed with a microwave pulse power of 700W for 60s.

[0040] S3, the hard carbon after microwave treatment was allowed to cool naturally at room temperature in the microwave oven to obtain 49.7g of hard carbon material.

[0041] Comparative Example 2

[0042] S1. Take 100g of thermosetting phenolic resin as a carbon source, put it into a graphite crucible, and heat it to 650℃ in a box furnace with a nitrogen flow of 10L / min and a heating rate of 5℃ / min and hold it for 2h to obtain 51.4g of hard carbon material with wide interlayer spacing.

[0043] Example 2

[0044] S1. Take 100g of thermosetting phenolic resin as a carbon source, put it into a graphite crucible, and heat it to 800℃ in a box furnace with a nitrogen flow of 20L / min and a heating rate of 20℃ / min and hold it for 12h to obtain 48.4g of hard carbon material with wide interlayer spacing.

[0045] S2, the 48.4g of hard carbon material with wide interlayer spacing obtained in S1 was placed in an argon atmosphere microwave oven and the surface groups were removed with a microwave pulse power of 700W for 240s.

[0046] S3, after microwave treatment, the hard carbon was allowed to cool naturally at room temperature in the microwave oven, resulting in 45.6g of hard carbon material with wide interlayer spacing and few surface functional groups.

[0047] Example 3

[0048] S1. Take 100g of thermosetting phenolic resin as a carbon source, put it into a graphite crucible, and heat it to 600℃ in a box furnace with a nitrogen flow of 5L / min and a heating rate of 1℃ / min and hold it for 1h to obtain 53.4g of hard carbon material with wide interlayer spacing.

[0049] S2, the 53.4g of hard carbon material with wide interlayer spacing obtained in S1 was placed in an argon atmosphere microwave oven and the surface groups were removed with a microwave pulse power of 700W for 30s.

[0050] S3, after microwave treatment, the hard carbon was allowed to cool naturally at room temperature in the microwave oven, resulting in 42.4g of hard carbon material with wide interlayer spacing and few surface functional groups.

[0051] Example 4

[0052] S1. Take 100g of thermosetting phenolic resin as a carbon source, put it into a graphite crucible, and heat it to 750℃ in a box furnace with a nitrogen flow of 15L / min and a heating rate of 15℃ / min and hold it for 10h to obtain 50.4g of hard carbon material with wide interlayer spacing.

[0053] S2, 50.4g of hard carbon material with wide interlayer spacing obtained in S1 was placed in an argon atmosphere microwave oven and the surface groups were removed with a microwave pulse power of 700W for 120s.

[0054] S3, after microwave treatment, the hard carbon was allowed to cool naturally at room temperature in the microwave oven, resulting in 48.1g of hard carbon material with wide interlayer spacing and few surface functional groups.

[0055] Example 5

[0056] S1. Take 100g of thermosetting phenolic resin as a carbon source, put it into a graphite crucible, and heat it to 600℃ in a box furnace with a nitrogen flow of 1L / min and a heating rate of 0.5℃ / min and hold it for 0.5h to obtain 55.4g of hard carbon material with wide interlayer spacing.

[0057] S2, the 55.4g of hard carbon material with wide interlayer spacing obtained in S1 was placed in an argon atmosphere microwave oven and the surface groups were removed with a microwave pulse power of 700W for 6s.

[0058] S3, after microwave treatment, the hard carbon was allowed to cool naturally at room temperature in the microwave oven, resulting in 52.6g of hard carbon material with wide interlayer spacing and few surface functional groups.

[0059] Figure 1 The XRD diffraction patterns of the hard carbon prepared in Example 1 and Comparative Example 1 of this invention clearly show that the hard carbon prepared at a low temperature of 650°C has a wider interlayer spacing of 0.399 nm, while the hard carbon prepared at a high temperature of 1500°C has a narrower interlayer spacing of only 0.354 nm. This is mainly attributed to the intense thermal motion of carbon atoms at high temperatures, which narrows the interplane spacing. Figure 2The first cycle curves of the hard carbon prepared in Example 1 and Comparative Example 2 of this invention at 100 mA / g clearly show that, under the same conditions, the hard carbon prepared with microwave treatment has a first coulombic efficiency of 90.2% for the sodium-ion half-cell anode, while the hard carbon material without microwave treatment has only a first coulombic efficiency of 55.6%. This is mainly attributed to the fact that the hard carbon material prepared at lower temperatures has a large number of surface groups. These groups react with lithium ions in the electrolyte during discharge, causing unnecessary lithium loss in the first cycle and resulting in low first coulombic efficiency. The non-thermal effect of microwave treatment (not exceeding 200°C) is insufficient to narrow the interlayer spacing of the hard carbon and can also eliminate the groups. Figure 3 The graph shows the rate performance of the hard carbon prepared in Example 1 and Comparative Example 1 at different current densities. The graph shows that the hard carbon prepared in Example 1 has reversible sodium storage capacity of 294, 270, 250, 200, 180, and 150 mAh / g at current densities of 0.1, 0.2, 0.5, 1, 2, and 5 A / g, respectively, while the hard carbon prepared in Comparative Example 1 has reversible sodium storage capacity of 263, 220, 160, 80, 40, and 20 mAh / g at current densities of 0.1, 0.2, 0.5, 1, 2, and 5 A / g, respectively. This is mainly attributed to the large interlayer spacing, which is suitable for the rapid insertion and extraction of sodium ions.

[0060] The hard carbon materials obtained in Examples 1, 1, and 2 were subjected to performance tests. The specific test procedures are as follows: (1) XRD test: The hard carbon powder was ground and sieved, placed in the sample stage and compacted and smoothed, and then placed in an XRD diffractometer for testing. The test angle was 10-80° and the scanning speed was 5° / min. (2) Electrochemical performance test: The hard carbon material was tested using a half-cell. The counter electrode was a sodium sheet, the separator was glass fiber, and the electrolyte was a 1M solution of NaPF6 dissolved in ethylene carbonate, diethyl carbonate, and dimethyl carbonate. The battery was assembled using a CR2032 coin-shaped battery case in a glove box filled with argon gas and with water and oxygen concentrations below 0.01ppm. In the charge-discharge test system, the charge-discharge test voltage was 0.01–2V.

[0061] In summary, the interplanar spacing of the hard carbon material prepared in Example 1 is 0.399 nm, which is significantly larger than that of the hard carbon material prepared in Comparative Example 1 (0.354 nm). This greatly improves the sodium storage efficiency of the hard carbon, giving the hard carbon of Example 1 excellent rate performance. It has reversible sodium storage capacities of 294, 270, 250, 200, 180, and 150 mAh / g at current densities of 0.1, 0.2, 0.5, 1, 2, and 5 A / g, respectively. In contrast, the hard carbon prepared in Comparative Example 1 has reversible sodium storage capacities of 263, 220, 160, 80, 40, and 20 mAh / g at current densities of 0.1, 0.2, 0.5, 1, 2, and 5 A / g, respectively. Example 1 shows that the hard carbon with fewer surface functional groups prepared has an ultra-high first coulombic efficiency of 90.2% at 100 mA / g, while the hard carbon prepared in Comparative Example 2, without microwave treatment to eliminate functional groups, has an first coulombic efficiency of only 55.6%. The hard carbon with functional groups eliminated by microwave treatment exhibits an ultra-high efficiency, and the non-thermal effect of microwave treatment (not exceeding 200°C) is insufficient to cause the hard carbon interlayer spacing to narrow. Therefore, the hard carbon prepared by this invention has a wide interlayer spacing and few surface functional groups, thus enabling it to have high first coulombic efficiency and excellent rate performance as a sodium-ion battery anode.

[0062] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0063] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined in this invention may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing hard carbon anode material for ultra-high rate performance sodium-ion batteries, characterized in that, Includes the following steps: S1 uses thermosetting phenolic resin as a carbon source, places it in a graphite crucible, and heats and holds it in a box furnace under a nitrogen flow to carbonize it. The holding temperature is 600-800℃, which can obtain hard carbon with a wide interlayer spacing. S2, the hard carbon with wide interlayer spacing obtained in S1 is subjected to microwave pulse treatment in an argon atmosphere microwave oven at a microwave temperature not exceeding 200°C for a preset time period to eliminate functional groups. S3, after microwave treatment, the hard carbon is naturally cooled to room temperature in the microwave oven to obtain a hard carbon sodium-ion battery anode material with wide interlayer spacing and fewer surface groups.

2. The method for preparing hard carbon anode material for ultra-high rate performance sodium-ion batteries according to claim 1, characterized in that, Specifically, S1 includes: the inert gas flow rate in the box furnace is 1-100 L / min.

3. The method for preparing hard carbon anode material for ultra-high rate performance sodium-ion batteries according to claim 1, characterized in that, Specifically, S1 includes setting the heat preservation time to 1-12 hours.

4. The method for preparing hard carbon anode material for ultra-high rate performance sodium-ion batteries according to claim 1, characterized in that, The microwave oven has a pulse power of 700 W.

5. The method for preparing hard carbon anode material for ultra-high rate performance sodium-ion batteries according to claim 1, characterized in that, The set pulse duration is 6-240 s.

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